Gene encoding the rat dopamine D4 receptor

ABSTRACT

A gene, flanking 5′ and 3′ sequences and derived cDNA encoding a rat D 4  dopamine receptor that is predominantly located in the cardiovascular and retinal systems is disclosed. The cDNA has been expressed in transfected mammalian cells and demonstrated to preferentially bind dopamine antagonists such as clozapine. The cDNA is useful as a probe for related D 4  dopamine receptors. Expressed in appropriate cell lines, it is useful as an in vitro screen for drugs which specifically bind to the receptor. Drugs that specifically bind to the receptor are then screened using standard methodology in rats, mice or dogs, for the physiological effects. Amino acids deduced from the determination of cDNA can be used to generate either polyclonal or monoclonal antibodies which recognize the D 4  receptor sequence but do not recognize D 1 , A 2 , D 3  or D 5  donpamenergic receptors, for use in immunocytochemical studies, identification and isolation via flow sorting of D4 expressing cell types. Antibodies could also be used to block or modify the effects of D4 agonists and/or antagonists. It is also demonstrated that selective stimulation or inhibition of some dopamine receptors, including D 4 , can be used to induce changes in the morphology of cells such as neurons.

[0001] The United States government has rights in this invention by virtue of a grant from the NIMH, grant number MH45019, to Richard D. Todd, principal investigator.

BACKGROUND OF THE INVENTION

[0002] The present invention is generally in the area of dopamine receptors, and is specifically a gene encoding a dopamine D₄ receptor, its flanking 5′ and 3′ sequences, and its derived cDNA, and methods of use thereof in screening for compounds having selective effects on the cardiovasculature and retinal tissues through interactions with the dopamine D₄ receptor.

[0003] Dopamine is an important neurotransmitter in the central nervous system (CNS), where it is thought to be involved in a variety of functions including motor coordination, reproductive regulation, and generation of emotions. A distinct peripheral dopaminergic system is thought to exist, although it is less well characterized. CNS dopamine receptors have historically been divided into two major classes, D₁and D₂, which can be distinguished by pharmacological, functional, and physical characteristics (Kebabian and Calne, (1979) “Multiple receptors for dopamine” Nature 277:93-96; Hamblin et al., (1984) “Interactions of agonists with D₂ dopamine receptors: evidence for a single receptor population existing in multiple agonist affinity-states in rat striatal membranes” Biochem. Pharmacol. 33:877-887; Seeman et al., (1985) “Conversion of dopamine of receptors from high to low affinity for dopamine” Biochem. Pharmacol. 34:151-154; Niznik, (1987) “Dopamine receptors: molecular structure and function” Mol. Cell. Endocrinol. 54:1-22). Peripheral dopamine receptors have been divided into DA1 and DA2 subgroups, which share some but not all pharmacological characteristics with their CNS counterparts (Goldberg and Kohli, (1987) “Identification and characterization of dopamine receptors in the cardiovascular system” Cardioloaia 32:1603-1607; Kohli et al., (1989) “Dopamine receptors in the stellate ganglion of the dog” Eur. J. Pharmacol. 164:265-272; Brodde, (1990) “Physiology and pharmacology of cardiovascular catecholamine receptors; implications for treatment of chronic heart failure” Am. Heart J. 120:1565-1572).

[0004] Molecular cloning techniques have revealed a diversity of CNS receptor subtypes in each class. All are members of the G protein-coupled receptor gene superfamily and have seven potential transmembrane (Tm) spanning domains. In contrast to most members fo the G-protein coupled receptor gene family, the D₂-like genes have multiple exons separated by introns both in the coding and non-coding regioins. Further diversity is generated by alternative splicing.

[0005] Prototypic D₂ ligand binding and signal transduction characteristics have been found for D₂ (Bunzow et al., (1988) “Cloning and expression of a rat D₂ dopamine receptor cDNA” Nature 336:783-787) and D₃ (Sokoloff et al., (1990) “Molecular cloning and characterization of a novel dopamine receptor (D₃) as a target for neuroleptics” Nature 347:146-151) receptors. The recently reported human D₄ receptor also has a D₂-like pharmacological profile (Van Tol et al., (1991) “Cloning of the gene for a human dopamine D₄-receptor with high-affinity for the antipsychotic clozapine” Nature 350-610-614). Two distinct D₁ receptors have also been cloned, called D₁ (Sunahara et al., (1990) “Human dopamine D₁ receptor encoded by an intronless gene on chromosome 5” Nature 347:80-83; Zhou et al., (1990) “Cloning and expression of human and rat D₁ dopamine receptors” Nature 347:76-80 ; Monsma et al., (1990) “Molecular cloning and expression of a D₁ dopamine receptor linked to adenylyl cyclase activatione” Proc. Natl. Acad. Sci. USA 87:6723-6727; Dearry et al., (1990) “Molecular cloning and expression of the gene for a human D₁ dopamine receptor” Nature 347:72-76) and D₅ (Sunahara et al., (1991) “Cloning of the gene for a human dopamine D₅ receptor with higher affinity for dopamine than D₁ . Nature 350:614-619). To date no peripheral dopamine receptor has been cloned, although it has been suggested that there is a low level of expression in D₃ in kidney (Sokoloff et al., 1990).

[0006] Van Tol et al. (1991) reported the isolation of a human D₄ receptor with a high affinity for the neuroleptic drug clozapine. Multiple variants of this dopamine receptor were also reported by Van Tol, et al., (1992) Nature 358, 149-154. These receptors were also the subject of PCT WO 92/10571 by State of Oregon. Although the function of these particular receptors was not identified, they are assumed to be important in binding drugs having anti-psychotic activity.

[0007] It is an object of the present invention to provide the gene, its flanking 5′ and 3′ sequences and the derived cDNA encoding another dopamine D₄ receptor present in rat cells.

[0008] It is a further object of the present invention to provide methods for expression and screening of compounds binding the new dopamine D₄ receptor.

[0009] It is another object of the present invention to provide a method for screening for compounds having cardiovascular activity and effects on retinal tissue which specifically bind to dopamine D₄ receptors.

[0010] It is still another object of the present invention to provide a means and method for modulation of the morphology of cells expressing D₄ receptors, and other dopamine receptors, by stimulation or inhibition of the receptors via exposure of the cells to specific compounds.

SUMMARY OF THE INVENTION

[0011] A gene, its 5′ and 3′ flanking sequences and the derived cDNA encoding a rat D₄ dopamine receptor that is predominantly located in the cardiovascular and retinal systems is disclosed. The gene has been expressed in transfected mammalian cells and demonstrated to preferentially bind dopamine antagonists such as clozapine.

[0012] The gene and/or cDNA is useful as a probe for related D₄ dopamine receptors. Expressed in appropriate cell lines, it is useful as an in vitro screen for drugs which specifically bind to the receptor. Drugs that specifically bind to the receptor are then screened using standard methodology in rats, mice or dogs, for the physiological effects. Antibodies to the protein are useful in immunocyt chemical studies, identification and isolation via flow sorting of D4 expressing cell types, and in blocking or modifying the effects of D4 agonists and/or antagonists.

[0013] Stimulation or inhibition of the D₄ receptor, D₂ receptor, or D₃ receptor, either in cells naturally expressing the receptor or which have been transfected with cDNAs encoding anyone or more of several dopamine receptors, has been demonstrated to allow modification of the cell morphology. In one example, the number and extent of branching of neurites in cells transfected with dopamine receptors is increased significantly by exposure to compounds selectively binding to the receptors.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 is a schematic of the sequence structure of the rat dopamine D₄ receptor gene. Coding regions are shown in black, noncoding regions are shown as clear boxes, and relevant restriction sites are indicated.

[0015]FIG. 2 shows the amino acid alignment of rat (rD4) and human (hD4) D₄ receptors.

[0016]FIG. 3 is a comparison of the structure of the Human D₄ receptor gene, which has an additional splice site, with the predicted structure of the rat D₄ gene. Oligonucleotides used for reverse transcription/PCR amplification are indicated. (B) Sequence of the cDNA generated by PCR amplification of reverse-transcribed rat atrial mRNA as described in the text. Identity and direction of the sequencing primers are indicated. Double lines to the right of the sequence indicate regions of identity with the human D₄ receptor sequence; thick lines demarcate transmembrane domains; the single line denotes non-identity of sequences between rat and human genes within the third cytoplasmic loop. The analogous location of the human exon 3/exon4 splice site is marked with an asterisk. The Tm VI splice site, which is conserved in all D₂-like receptors isolated to date, is indicated by an arrowhead.

[0017]FIG. 4 is a pharmacological analysis of transfected rat D₂₄₄₄ and D₄ receptors and human D₃ receptors in CCL1.3 cells. FIG. 4A is graph of [³H]-spiperone (%) versus log [eticlopride, M]. FIG. 4B is a graph of [³H]-spiperone (%) versus log [(+)butaclamol, M]. FIG. 4C is a graph of [³H]-spiperone (%) versus −log [clozapine, M]. The rat D₄ gene, the rat D₂₄₄₄ cDNA and the human D₃ cDNA were inserted into the expression vector pcDNA/neo and transfected into CCL1.3 cells. Subclones expressing the mRNAs were expanded in medium containing G418 and assayed for competition of 1 nM [³H]spiperone binding by eticlopride, (+)butaclamal and clozapine, as described in Materials and Methods. Open circles, D₄-expressing cells; closed circles, D₂₄₄₄-expressing cells, triangles, D₃-expressing cells. Results are shown as mean ± SD of percent of specifically bound [³H]spiperone remaining for an experiment done in triplicate. The apparent K₁'s for the D₄, D₂₄₄₄ and D₃ receptors, respectively, were: 27.0±2.9 nM, 0.067±0.21 nM and 0.16±0.02 nM, for eticlopride, 51.3±17.5 nM, 0.69±0.15 nM; and 11.2±0.8 nM for(+) butaclamal; 41.7±6.1 nM, 142.5±4.3, and 620±51.6 nM for clozapine (mean± SEM for these experimentsa.

[0018]FIGS. 5A, B, C and D, are bar graphs of neurite number (FIG. 5A), branch number (FIG. 5B), primary neurite length (FIG. 5C), and total neurite extent (FIG. 5D), in percent change following quinpirole stimulation for control MN9D cells, and D2₄₄₄, D₃, and D₄ transfected cells. The data of three separate experiments for each of the four cell types are expressed as the average percent change± SEM from control (unstimulated) cells. Cell numbers for the individual experiments were 100 for each condition except for one experiment each for the D3 and D4 receptor expressing cells, in which there were 59 and 38 cells for each condition respectively. The cells were plated at low density and cultured for 90 to 95 hours with or without 2 μM quinpirole. Significant changes are indicated by filled bars. Open bars represent non-significant changes.

[0019]FIG. 6 is a comparison of control and quinpirole treated cells. Cells from E15 rat mesencephalon were plated at high density, incubated for 12 hours, and cultured for 90 hours in the presence (quinpirole) or absence (control) of 2 μM quinpirole. Cultures were then fixed and dopamine synthesizing cells identified by tyrosine hydroxylase immunoreactivity. Figure shows camera lucida drawings of tyrosine hydroxylase expressing cells in confluent cultures. There are five TH positive cells in the control condition and three TH positive cells in the quinpirole condition. In the presence of quinpirole TH positive cells were larger, have more branch points and much more extensive growth cone elaboration.

DETAILED DESCRIPTION OF THE INVENTION

[0020] Dopamine receptors have been implicated in a variety of neurological and neuropsychiatric disorders. The polymerase chain reaction and low stringency library screening were used to isolate a rat genomic clone encoding a new dopamine receptor. Sequence data and pharmacological analysis reveal this clone is the rat analog of the human D₄ receptor, which exhibits a high affinity for the antipsychotic drug clozapine. The mRNA for this receptor shows a restricted pattern of expression in the central nervous system. Significant levels of expression were found in the hypothalamus, thalamus, olfactory bulb, and frontal cortex. However, 20-fold higher levels of D₄ mRNA expression were observed in the cardiovascular system. High levels are also expressed in the photoreceptor layer of the retina. Stimulation of this receptor in the dark leads to a marked decrease in the light sensitive pool of cAMP. Thus, this receptor appears to mediate dopamine function in the cardiovascular and retinal system as well as the central nervous system.

[0021] The creation of a transfected mouse fibroblast cell line that expresses a ligand-specific receptor with the pharmacological profile of a D₂ subtype has been reported by Todd et al., (1989) “Cloning of ligand-specific cell lines via gene transfer: identification of a D₂ dopamine receptor subtype” Proc. Natl. Acad. Sci. USA 86:10134-10138. As one strategy in the isolation of these sequences, a rat genomic library was screened with Tm-specific probes derived from D₂ (Bunzow et al., 1988) and D₃ (Sokoloff et al., 1990) consensus sequences. Using this approach, D₁, D₂, and D₃ rat genomic clones, as well as a clone of an unknown receptor that had a high degree of structural identity with D₂ and D₃ receptor genes, were identified. Sequence data and pharmacological analyses demonstrated that this was the rat equivalent of the human D₄ gene of Van Tol (1991), although significant differences, as shown below, exist between the human and the rat genes. and the human gene cannot be used to isolate the-rat gene. The highest levels of expression of the rat analog of the human D₄ “clozapine” receptor are found in the heart and the proximal aortic arch.

EXAMPLE 1 Isolation and Characterization of the Rat D₄ Gene

[0022] The isolation and characterization of the gene and cDNA encoding the rat D₄ dopamine receptor will be further understood by reference to the following detailed description.

Materials and Methods Isolation of the Rat D₄ Gene

[0023] A lambda Dash rat spleen genomic library (Stratagene) was screened for D₂-like receptor sequences with the use of radiolabeled Tm II, III, and VI/VII probes. oligonucleotides encompassing the indicated domains were derived from consensus sequences from the rat D₂ (Bunzow et al., 1988) and D₃ genes (Sokoloff et al., 1990). Labeling of probes, hybridization, and washing were performed according to standard methodologies, for example, as described by Sambrook et al., (1989): Molecular Cloning: A Laboratory Manual. Cold Spring Harbor, N.Y., Cold Spring Harbor Laboratory; and Feinberg and Vogelstein, (1984) “A technique for radiolabeling DNA restriction endonuclease fragments to high specific activity” Anal. Biochem. 137:266-267. Hybridization-positive clones were further characterized by amplification using the polymerase chain reaction (PCR) with gene-specific probes derived from coding and intron sequences of the rat D₂ gene (O'Malley et al., (1990) “Organization and expression of the rat D2_(A) receptor gene: identification of alternative transcripts and a variant donor splice site” Biochemistry 29:1367-1371), the rat D₃ gene (Sokoloff et al., 1990), and the rat D₁ gene (Monsma et al., 1990). Hybridization-positive, PCR-negative clones were plaque purified and further characterized. A 3.8-kb BamHI fragment common to the seven clones that were Tm VI/VII-positive but not identified as D₂, D₃, or D₁, was subcloned and sequenced using the method of Chen and Seeburg (1985) “Supercoil sequencing: a fast and simple method for sequencing plasma DNA” DNA 4:165-170. DNA sequence analysis was performed with computer programs generated by Intelligenetics. The reported sequences are available from GenBank under accession number M84009.

[0024] The cDNA a sequence and derived gene for rat dopamine D₄ receptor is shown as Sequence ID No. 1. The deduced amino acid sequence is shown as Sequence ID No. 2.

Expression Vectors

[0025] A full-length D₂₄₄₄ cDNA clone (2.3 kb) was isolated from a rat striatal library and subcloned into the HindIII site of pcDNA/neo. A genomic D₄ fragment generated by partial NarI digestion and complete BamHI digestion was made blunt ended and ligated into the EcoRV site of pcDNA/neo. The D₄ gene in the expression vector started at nucleotide -5 and stopped 336 bp 3′ of the stop codon. DNA was purified as described by Gandelman et al., (1990) “Species and regional differences in the expression of cell type specific elements at the human and rat tyrosine hydroxylase gene loci” J. Neurochem. 55:2149-2152, for transfection.

Cell Culture and Transfection

[0026] Mouse CCL1.3 tk fibroblasts were grown in DMEM media supplemented with 10% fetal bovine serum. Cells were plated at a density of 3×10⁶ cells/10-cm dish, 12 to 24 h prior to transfection. Each plate of cells was transfected with 20 μg of plasmid DNA by CaPO₄ precipitation, using the method of Chen and Okayama (1987) “High efficiency transformation of mammalian cells by plasmid DNA” Mol. Biol. 7:2745-2752. Four hours after transfection, cells were shocked with 20% glycerol in DMEM for 2 min, and 48 h later the cells were split and placed in fresh media supplemented with 400 μg/ml of G418 (Geneticin, Gibco, active concentration). After two weeks, G418-resistant colonies were isolated with micropipette tips and screened for expression of D₂₄₄₄ or D₄ mRNA by reverse transcription/PCR analysis. Subclones expressing high levels of D₂₄₄₄ or D₄ mRNA were expanded and further characterized.

Binding Studies

[0027] Mouse fibroblasts expressing D₂₄₄₄ and D₄ were grown to 70% confluence and then harvested by scraping. After they had been washed twice in PBS, the cell pellets were resuspended in distilled water and ruptured by homogenization with a Brinkman Polytron, at setting 6 for 10 sec. Nuclei were removed by centrifugation for 5 min at 600 g. Membranes were pelleted by centrifugation for 25 min at 50,000 g. The pellets were resuspended in water and frozen at −70° C. until assayed. For receptor binding assays, samples containing 150 μg of membrane protein were aliquoted into glass test tubes. [³H]-Spiperone (1 nm) and varying concentrations of competing compounds were added in a final volume of 1 ml and a final buffer of 1.5 Mm CaCl₂, 5 mM MgCl₂, 5 mM KCl, 120 mM NaCl, 50 mM Tris-HCl, pH 7.4 at 20° C. The tubes were incubated for 15 min at 37° C., and the assays were terminated by addition of 5 ml of ice-cold 50 Mm Tris-HCl buffer (pH 6.9), collected onto glass-fiber filters, and washed twice with the same cold buffer in a modified Brandel cell harvester. The radioactivity retained on the filters was counted in a Beckman LS 1701 scintillation counter.

Oligonucleotides

[0028] Oligonucleotide primers were synthesized on an Applied Biosystems synthesizer. The Tm VI/VII primer set included orD-403, 5′-TGCTGGCTGCCCTTCTTC-3′ (Sequence ID No. 5), which is identical to sequences within Tm VI in both D₂ and D₃ genes, and orD-404, 5′-GAAGCCTTGCGGAACTC-3′ (Sequence ID No. 6), which is complementary to sequences from TM VII. For tissue distribution studies total RNA was reverse transcribed using orD₄-515, 5′-CTGTCCACGCTGATGGCG-3′ (Sequence ID No. 7), which is complementary to nucleotides 366 to 383 shown in Sequence ID No. 1. Second strand synthesis and further amplification utilized orD₄-465 and orD₄-466, 5′ CAGACACCGACCAACTA-3′ (Sequence ID No. 8), which is identical to nucleotides 187 to 204. Additional oligonucleotides included orD₄-474. 5′-TGACACCCTCATGGCCAT-3′ (Sequence ID No. 9), which is identical to nucleotides 309 to 326; orD₄-465, 5′-TTGAAGATGGAGGGGGTG-3′ (Sequence ID No. 10), which is complementary to nucleotides 342 to 359; orD₄-501, 5′-GCACACCAAGCTTCACAG-3′ (Sequence ID No. 11), which is identical to nucleotides 657 to 674; and orD₄-506, 5′-TTGAAGGGCACTGT-TGACATAGC-3′ (Sequence ID No. 12), which is complementary to nucleotides 1064 to 1085. Oligonucleotides used for in situ hybridization included orD-502, 5′-ATGGTGTTGGCAGGGAAC-TCGCTC-3′ (Sequence ID No. 13), which is identical with nucleotides 124 to 193, and orD-499, 5′-GAGCGAGTTCCCTGCCAACACCAT-3′ (Sequence ID No. 14), which is complementary to the same nucleotides.

mRNA Analysis by PCR

[0029] Total RNA was isolated from various tissues using the method of Chomczynski and Sacchi (1987) “Single-step method of RNA isolation by acid guanidium thiocyanate-phenol-chloroform extraction” Anal. Biochem. 162:156-159, reverse transcribed using the method of Krug and Berger (1987) “First-strand cDNA synthesis primed with oligo(dT)” Methods Enzymol. 152:316-325, and further amplified as described by O'Malley et al. (1990). Amplification temperatures were: denaturation at 93° C. for 1 min, annealing at 52° C. for 1 min, and synthesis at 72° C. for 1 min for 30 cycles. PCR products were transferred to nylon after electrophoresis in 5% polyacrylamide gels. Filters were probed with an end-labeled oligonucleotide, orD₄-474, corresponding to sequences that are internal to the amplification set. Filters were hybridized and washed according to the manufacturer's protocol (Schleicher and Schuell). The MRNA levels were normalized for equal amounts of the 18S fragment of ribosomal RNA by Northern blotting followed by hybridization with an 18S gene fragment, using the method of Chan et al., (1984) “The nucleotide sequence of a rat 18S ribosomal ribonucleic acid gene, and a proposal for the secondary structure of 18S ribonucleic acids” J. Biol Chem 259:224-230.

In Situ Hybridization

[0030] Sense and antisense D₄ oligonucleotide probes were end-labeled with digoxigenin-derivatized dUTP according to the manufacturer's protocols (Boehringer-Mannheim). Hybridization conditions were essentially as described by Springer et al., (1991) “Non-radioactive detection of nerve growth factor receptor (NGFR) mRNA in rat brain using in situ hybridization histochemistry” J. Histochem. Cytochem. 39:231-234. The probe concentration was 35 ng/ml, and hybridization was overnight at 37° C. The final stringency wash was 0.5×SSC, 22° C. for 30 min.

Results

[0031] Low stringency screening of genomic libraries with Tm-specific probes was performed in order to isolate additional members of the dopamine D₂ receptor family. Because there are regions of very high identity between D₂ and D₃, notably within Tm domains II and III (100% amino acid identity) and Tm VI and VII (70% and 87% amino acid identity, respectively), it was reasoned that DNA fragments specific for the region encoding each transmembrane sequence might be useful in identifying other members of the D₂-like receptor family. In addition, a comparison of the structure of the rat D₂ gene (O'Malley et al., 1990) with that of the D₃ gene (Sokoloff et al., 1990; Giros et al., (1991) “Shorter variants of the D₃ dopamine receptor produced through various patterns of alternative splicing. Biochem. Biophys. Res. Commun. 176:1584-1592) indicated a high degree of conservation in the intron-exon boundaries of these genes. Therefore, Tm specific probes were constructed so as to not cross these sites, so that genomic DNA could be used as a template. Domain-specific oligonucleotides were synthesized and DNA amplification methodology used to create double-stranded DNA starting with rat genomic DNA as a template. Fragments of the appropriate size were gel purified, radiolabeled, and hybridized to a rat genomic library. The number of phage screened corresponded to 15 rat genomes of inserted DNA.

[0032] The results of screening the same set of filters successively with the Tm II, III, and VI/VII probes are shown in Table 1. TABLE 1 Results of screening a rat genomic library with degenerate oligonucleotides encompassing transmembrane domains II, III, and VI/VII. Number of clones of each type identified by PCR* Probe D1 D2 D3 D4 TM II 13 38 24 0 TMIII 7 43 20 0 TM VI/VII 0 21 25 7

[0033] The feasibility of the strategy is evident from the detection of D₁ and D₃ using the indicated probes. No unknown dopamine receptors were detected with the Tm II and III probes, suggesting either that additional receptors have less identity in these domains or that these probes are too biased towards D₂/D₃ sequences. Probes to Tm domains I, IV, and V were not made, since there is only limited identity between D₂ and D₃ in these regions and no conservation of splice boundaries. Instead, the library was screened with the Tm VI/II probe. The majority of the 53 positive clones were D₂ and D₃. However, seven clones were clearly different and were further characterized. DNA from the seven isolates was digested with several restriction enzymes, blotted, and probed with the TM VI/VII probe. The smallest hybridizing fragment was subcloned into Bluescript and sequenced with the Tm VI/VII PCR primers.

[0034] Translated sequences revealed two hydrophobic domains that had 62% and 64% identity to D₂ and D₃, respectively, as well as a splice site in exactly the same position as in these genes, as described by Sokoloff et al., 1990; and O'Malley et al., (1990). Specific primers were designed from this sequence and used in unsuccessful screens of several cDNA libraries by the polymerase chain reaction (PCR), including libraries prepared from basal ganglia, hypothalamus, fetal brain, and pituitary. Subsequently, a battery of D₂ and D₃ primers derived from Tm domains I through V against the D₄ genomic clone were tested. They all seemed to hybridize to the same 3.8-kb BamHI fragment containing Tm regions VI and VII, suggesting that the new gene was very small in comparison with D₂ and D₃. Further sequence data confirmed this premise, revealing an overall gene structure of four exons and three introns spanning approximately 3500 bp, as shown in FIG. 1 B

[0035] Comparison of the structural features and nucleotide S sequence of the human D₄ receptor (Sequence ID No. 3, nucleotide sequence, and 4, deduced amino acid sequence) isolated from a human neuroblastoma cell line, as described by Van Tol and coworkers (1991), indicated that the new receptor is the rat analog of the D₄ receptor. The pharmacological profile of the human clone has confirmed its D₂-like nature and suggested that this receptor has a very high affinity for clozapine (5- to 15-fold higher than the D₂ receptor; Bunzow et al., (1988); Van Tol et al., 1991).

[0036] In the coding regions, the rat gene (Sequence ID No 1) shares 73% amino acid and 77% nucleic acid sequence homology with the human D₄ gene (Sequence ID No 3). In contrast, the rat and human D₂ receptors share 95% amino acid and 90% nucleic acid identity (Mack et al., (1991) “The mouse dopamine D2_(A) receptor gene: sequence homology with the rat and human genes and expression of alternative transcripts” J. Neurochem. 57:795-801). As shown in FIG. 2, there is between 89% and 96% identity within the transmembrane domains of these genes. Most of the differences between rat and human D₄ genes occur in the third intracytoplasmic loop where there is only 50% amino acid identity. In the human, this region encompasses an unusual splice junction within intron 3 of the D₄ gene: instead of a canonical GT/AG donor/acceptor site, a TC/CT is indicated, as reported by Van Tol et al., (1991). This unconventional splice site is not observed in the rat gene.

[0037] The strategy depicted in FIG. 3A was used in order to rule out the presence of a small intron, less than 30 bp, with a different unusual splice site. oligonucleotides were chosen flanking the bona fide slice site within Tm VI (o056) and the putative splice site within the third cytoplasmic loop (o501). Amplification of genomic DNA would result in a 618-bp fragment when these primers are used. The proposed model of the rat D₄ gene predicts a 426-bp band for the cDNA. Rat atrial RNA was reverse transcribed with the use of primer o506, then PCR amplification was performed with the 501/506 primer set. A single band of 426 bp was obtained, which was subcloned and sequenced. FIG. 3B demonstrates the presence of the Tm VI splice site and the absence of any additional splice sites within this sequence. Therefore, the rat D₄ gene has four exons encoding an open reading frame of 368 amino acids.

EXAMPLE 2 Pharmacological Confirmation That the Putative Rat D₄ Gene Codes for A D₄ Receptor

[0038] To confirm that the putative rat D₄ gene codes for a dopamine receptor analogous to the human D₄ receptor, the rat gene was inserted into the expression vector pcDNA/neo and transfected into the CCL1.3 fibroblast cell line, which was then screened for [³H]-spiperone binding. Transfected cells were enriched by expansion in medium containing G418. The rat D₂ cDNA and the human D₃ cDNA were expressed in the same cell line. The results of the [³H]-spiperone binding studies are shown in FIGS. 4A, 4B, and 4C.

[0039] As determined by displacement with 1 μM eticlopride, specific binding of 2 nM [³H]-spiperone was about 50% of the total bound counts for all three receptors. Similar to the results reported by Van Tol et al. for the human receptors, the rat D₂ receptor has a higher affinity for eticlopride and (+)butaclamol while the rat D₄ receptor has a 2- to 3-fold higher affinity for clozapine. The human D₃ receptor also has a higher affinity for eticlopride and (+) butaclamol and a much lower affinity for clozapine than the rat D₄ receptor. The relative rank order potency of these three compounds for the three receptors, however, demonstrates that the rat D₄ gene codes for a dopamine receptor analogous to the human D₄ gene.

Distribution of D₄ mRNA

[0040] Total RNA (250 μg) from the indicated regions was isolated, reverse transcribed, and amplified using primers flanking the first intron. PCR products were separated by electrophoresis, blotted onto nylon filters, and hybridized with an oligonucleotide internal to the PCR primers. Regions tested include adrenal medulla, adrenal cortex, occipital cortex, temporal/parietal cortex, frontal cortex, olfactory bulb, basal ganglia, hippocampus, medulla, thalamus, cerebellum, and mesencephalon. One microgram of hypothalamic total RNA and 250 ng of atrial and ventricle RNA were treated as described above, except that primer or D4-465 was used. This primer generates a 171-bp product.

[0041] Various CNS and peripheral tissues were examined for the presence and relative abundance of D₄ transcripts. Total RNA was reverse transcribed with a D₄ exon 2-specific primer, and this procedure was followed by second strand synthesis and DNA amplification. The predicted D₄ PCR product of 195 bp is detected in only a few central nervous system regions such as olfactory bulb, frontal cortex, and hypothalamus. Surprisingly, the D₄ PCR product is at least 20-fold more abundant in heart than in the CNS but is not detectable in liver, adrenal cortex, adrenal medulla, or kidney. Within the heart, D₄ is more abundant in the atrial/large vessel region. In separate experiments, mouse retinas were examined for the presence of D₄ transcripts and D₄ MRNA was found to be abundantly expressed in this tissue as well (Cohen, A. I., et al., (1992) “Photoreceptors of mouse retinas possess D₄ receptors coupled to adenylate cyclase” Proc. Natl. Acad. Sci. USA 89, 12093-12097).

[0042] To confirm and extend these results, digoxigenin-labeled oligonucleotide probes were used for in situ hybridization histochemistry. Sense and antisense oligonucleotides were end-labeled with digoxigenin-derivitized dUTP and hybridized to 20 μm frozen sections of heart and brain from 6- to 8-week-old male Sprague-Dawley rats. The hybridized oligonucleotides were visualized by alkaline phosphatase-linked anti-digoxigenin antisera and counterstained with eosin. Color development was for 16 h. Sections through the proximal aorta show intense staining of aorta. Color development was for 22 h. There was scattered hypothalamic staining in the region of the arcuate nucleus and the ventromedial nucleus of the hypothalamus, only a few positive cells in the striatum, no positive cells in the hippocampus, and the scattered presence of positive cells in the thalamus.

[0043] In the CNS, D₄ mRNA-positive cells were found primarily in hypothalamic areas surrounding the third ventricle. The hypothalamic distribution overlaps, but is not restricted to, the A11, A13, and A14 groups of hypothalamic dopaminergic cell bodies. Few positive cells were observed in the basal ganglia, hippocampus, or cortical regions. In the heart, heavily labeled cells predominated in the proximal aorta and the outflow tract of the left ventricle, with scattered positive cells throughout the central fibrous body. With more sensitive color development conditions, the predominant atrial expression of D₄ mRNA detected by PCR is evident. The distribution of staining is most consistent with the expression of D₄ mRNA in vascular smooth muscle and cardiac myocytes. D₄ mRNA was also identified in the retinal neuronal and photoreceptor layer in mouse (Cohen, et al., 1992).

[0044] The relatively high affinity of the human D₄ receptor for the neuroleptic drug clozapine, as reported by Van Tol et al., (1991), has generated interest in the possibility that this site is responsible for clozapine's novel antipsychotic effects. Clozapine also has significant tachycardia and hypotensive side effects. These have generally been ascribed to antagonist interactions at muscarinic acetylcholine receptor sites, as reported Fitton and Heel, (1990) “Clozapine. A review of its pharmacological properties, and therapeutic use in schizophrenia” Drugs 40:772-747. In the periphery, however, relatively selective D₂-like agonists, such as piribedil, can cause vasodilation, hypotension, and bradycardia, as reported by McCoy et al., (1986) “Selective antagonism of the hypotensive effects of dopamine agonists in spontaneously hypertensive rats” Hypertension 8:298-302. These effects appear to be due at least in part to inhibition of sympathetic nerve activity, Hohli et al., (1989), and can be blocked by peripheral D₂-like antagonists such as domperidone. Within the heart, D₂-like receptor stimulation has positive inotropic effects, Zhao et al., (1990) “Effects of dopamine D₁ and dopamine D₂ receptor agonists on coronary and peripheral hemodynamics” Eur. J. Pharmacol. 190:193-202. The demonstration of high levels of expression of D₄ MRNA in the cardiovascular system indicates that some of these effects may be secondary consequences of binding to peripheral D₄ Dopamine receptors and that clozapine may be a prototypic model for a new class of receptor-selective agents for the treatment of cardiovascular disorders. Of particular interest is the recent mapping of the locus for a familial form of the long Q-T syndrome to the vicinity of H-ras-1 on chromosome lip, as reported by Keating et al., “Linkage of a cardiac-arrhythmia, the long QT syndrome, and the Harvey Ras-1 gene” Science 252:704-706 (1991). This is also the location of the human D₄ receptor gene, as reported by Gelernter et al., “DrD4, the D₄ dopamine receptor, maps to distal 11p” Am. J. Hum. Gen. 49:340 (1991). It is possible that an abnormality of the D₄ receptor may be responsible for this cardiac conduction disorder.

[0045] In summary, it was found that the rat D₄ receptor MRNA was expressed at low levels in several central nervous system regions but at much higher levels in the heart and retina. In situ hybridization studies are consistent with a hypothalamic autoreceptor function for the D₄ receptor in the central nervous system. The major site of expression, however, was in atrial and vascular myocytes. Therefore, the D₄ receptor, unlike the other D₂-like subtypes, may be predominantly a peripheral dopaminergic receptor. Accordingly, this receptor should be useful as a specific receptor for dopamine antagonists such as clozapine as well as dopamine agonists. By virtue of this specificity, many of these compounds can be used as regulators of blood pressure and heart rate. Depending on whether such compounds are agonists or antagonists, blood pressure may be raised or lowered and heart rate slowed or quickened. In addition, such compounds would increase or decrease, respectively, the efficiency of cardiac contractions (i.e., positive or negative inotropic effects). Similarly, such agonists and antagonists would decrease or increase light-sensitive pools of cAMP in retinal photoreceptors and effect the functioning of the eye. Effective dosages are determined based on the known dosages for these compounds for treatment of other disorders, screening for binding to cells expressing D₄ receptors, extrapolation to treatment of specific conditions, and other techniques known to those skilled in the art.

EXAMPLE 3 Morphogenic Potentials of D2, D3, and D4 Receptors

[0046] As discussed above, molecular cloning studies have defined a family of dopamine D₂-like receptors (D₂, D₃, D₄), which are the products of separate genes. Stimulation of dopamine D₂-like receptors in cultures of fetal cortical neurons increases the extension and branching of neurites (Todd, R. D. (1992) Biol. Psych 31, 794-807). To determine which D₂-like receptors possess morphogenic potentials, a clonal mesencephalic cell line (MN9D) was transfected with D₂, D₃, or D₄ receptor subtypes, treated with the D₂ agonist quinpirole, and changes in morphology quantitated.

[0047] The results demonstrated that stimulation of D₂ receptors increased the number and branching of neurites, with little effect on neurite extension, while stimulation of D₃ and D₄ receptors increased the branching and extension of neurites. These effects on neuronal morphology could be blocked by the dopamine D₂-like receptor antagonist eticlopride. These results suggest that all of the known D₂-like receptors may have specific developmental roles in regulating neuronal morphogenesis of dopaminergic pathways. The types of morphological effects seen suggest that developmental abnormalities of stimulation of these receptor subtypes may result in the neuroanatomical changes found in many neurological and psychiatric disorders such as mental retardation syndromes, schizophrenia, affective disorders and autism. Regulation of receptor subtype stimulation by agonists or antagonists during pre- or postnatal life may therefore be an effective form of treatment to prevent or reverse the development of anatomical abnormalities and these diseases.

Methods Transfection

[0048] Different dopamine receptor cDNAs or genes were transfected into the dopamine containing mesencephalic cell line, MN9D. MN9D is a cell line produced by fusion of fetal mouse mesencephalic cells with N18TG2 neuroblastoma cells, described by Choi, H., et al. (1991) Brain Res. 552, 67-76. The MN9D cell line is a stable immortalized clonal cell line established by fusion of the neuroblastoma cell N18TG2 with embryonic mouse mesencephalic dopamine producing neurons. Some of the characteristics of these cells include: the synthesis and release of dopamine; neurite formation and immunoreactivity; production of large voltage-sensitive sodium currents generated by depolarization; sensitivity to MPTP, a dopaminergic neurotoxin, and the ability to distinguish between the presence of dopaminergic target and non-target cells. Additionally, neither the MN9D nor the CCL1.3 cell lines have detectable mRNA or expressed protein for any of the D₁-like or D₂-like receptors.

[0049] The exon 6 containing form of the rat D2 receptor (D₂₄₄₄) (O'Malley, et al., “Organization and Expression of the rat D_(2A) receptor gene: identification of alternative transcripts and a variant donor splice site” Biochem. 29:1367-1371 (1990)) (Sequence ID No. 15) and the human D3 receptor cDNA (Giros, et al., C.R. Acad. Sci. (Paris) III, 311, 501-508 (1990)) (Sequence ID No. 16) were inserted into the mammalian expression vector pcDNA/neo (Invitrogen). The entire rat D4 (Sequence ID No. 1) receptor gene was inserted into the same vector. All three plasmids were transfected into MN9D cells using the glycerol shock/calcium phosphate technique of Wigler, M., et al. (1979) Cell 16, 777-786; and Graham, F. and van der Eb, A (1973) Virology 52, 456-467, and permanent, clonal transfectants selected by G-418 resistance and limiting dilution. The clonal cell lines were assayed for expression of receptor mRNAs by reverse transcription of total cellular RNA with receptor specific oligonucleotides, followed by DNA amplification (O'Malley, K. L., et al, 1990) (RT/PCR) and for receptor protein by [³H]-spiperone binding (Todd, R. D., et al, 1989). Each clonal cell line expressed only the transfected dopamine receptor mRNA and the expressed receptor proteins displayed the predicted pharmacological differences for D₂, D₃, and D₄ receptors. The average number of expressed receptors per cell for the D₂₄₄₄, D₃, and D₄ expressing cell lines were about 45,000, 15,000, and 3,500 respectively.

Morphology

[0050] The parental and transfected cell lines were plated at low density (8 cells/mm²) onto poly(D-)lysine coated 35 mm culture dishes (Corning). The medium was Dubecco's Modified Eagle's Media (Gibco) containing 10% fetal bovine serum. 0.05% (w/v) G-418, an antibiotic which selects for the transfected cells, was added to the medium for selection. The cells were cultured in a humidified incubator under 10% CO₂ with or without 1-2 μM quinpirole, a non-toxic D2-like receptor agonist.

[0051] To determine whether the stimulatory effects of quinpirole on neurite outgrowth could be blocked if mediated by dopamine D₂-like receptors, cells were co-cultured with 2 μM quinpirole and 1 μM eticlopride, a D₂-like receptor antagonist. K_(i)s (nM) for quinpirole are 4700±82 (D2₄₄₄), 1567±247 (D3), 453,3±71.0 (D4); K_(i)s(nM) for eticlopride 0.029±0.004 (D2₄₄₄), 0.46±0.12 (D3) 22.3±1.9 (all values are mean ± SEM of triplicate determinations for three to five individual assays).

[0052] Based on the K_(i) values, the micromolar concentrations of both quinpirole and eticlopride were expected to have stimulatory or inhibitory effects at each of the D₂-like receptors, respectively.

[0053] Cells were plated at low density, cultured overnight without treatment, then drugs or medium were added to the cultures. Quinpirole was added every 12 hours since this reagent quickly oxidizes. Eticlopride was added every 24 hours, and the control cultures received an equal amount of medium at the same time as the quinpirole additions. Living cells were photographed after 90 to 115 hours in culture using phase contrast microscopy (Nikon Diaphot) or a digital image processing system (Image-1). Morphologies of individual cells were quantitated at 1600× using a computer-interfaced drawing system with a digitizing light pad (Bioquant) as described by Todd, 1992; Sikich, L., Hickok, J. M., and Todd, R. D. Dev. Brain Res. 56, 269-274, 1990). Cells were measured consecutively over two to three dishes without knowledge of the treatment condition. Processes shorter than 5 μm were not reliably remeasured and were excluded from morphometric analysis.

Results

[0054] Transfection and subsequent agonist stimulation of dopamine D₂₄₄₄, D₃, and D₄ receptors in MN9D cells results in distinct changes in cell morphology. These persist for at least seven days in culture and can be blocked by dopamine D2-like antagonists.

Transfection Alters MN9D Morphology

[0055] The MN9D parent cell line which does not express either D₁- or or D₂-like receptors, and the transfected cells lines expressing D₂₄₄₄, D₃ and D₄ receptors, elaborate neurites in culture. Unstimulated cells can be distinguished from one another less than 12 hours after plating and all the cell lines continue to develop in morphologically distinct manners for at least two weeks in culture. As shown for a single experiment in Table 2 (minus quinpirole), D₂₄₄₄ expressing cells tend to have more neurites and a larger neuritic extent. D₃ expressing cells have marked increases in neurite number, branch number and total neuritic extent, and D₄ expressing cells most closely resemble the parent MN9D cell line. TABLE 2 Effect of Quinpirole on Cell Morphology Transfected MN9D Cells MN9D D2₄₄₄ D3 D4 Quinpirole − + − + − + − + Number of Cells 100 100 100 100 59 59 100 100 Neurite Number 3.25 ± .21   4.25 ± .23^(§)* 3.98 ± .21 4.72 ± .23 4.45 ± .29 4.64 ± .26  3.73 ± .23 4.12 ± .23  per Cell (μm) Branch Number  .69 ± .16  .63 ± .12  .66 ± .15  2.35 ± .35^(§) 1.91 ± .35 3.51 ± .34⁺  .51 ± .17 2.10 ± .29^(†) per cell (μm) Primary Neuritic 24.54 ± 2.07 22.94 ± 2.01 31.30 ± 6.21 30.09 ± 2.02 32.50 ± 5.90 54.24 ± 6.69^(†) 21.56 ± 1.62 59.82 ± 6.7^(‡)  Length (μm) Total Neuritic 59.75 ± 5.74 63.29 ± 4.39 78.22 ± 9.62 104.48 ± 8.95*  96.10 ± 12.34 157.77 ± 13.94⁺ 58.00 ± 5.43 140.53 ± 13.56^(‡) Length (μm)

[0056] The cells were cultured with or without 2 μM quinpirole for 91-93 hours, photographed, and morphologies quantitated. All measurements were made without knowledge of the treatment condition and are expressed as means ± SEM. In these analyses only neurites and neurite branches longer than 5 μM were included because of poor interrater reliability at shorter lengths. Statistical comparisons are shown for the effects of quinpirole on each individual cell lines. Since not all morphological characteristics were normally distributed all statistical analyses were non-parametric and are corrected for the number of comparisons. Significant differences from no added quinpirole condition (Mann-Whitney U test):^(·)p<10⁻²; §p<10⁻³; ⁺p<10⁻⁴; †p<10⁻⁵; ‡<10⁻⁶. MANOVA post hoc comparisons of morphological characteristics between cell lines are shown in Table 3. TABLE 3 Comparisons of neurite outgrowth between the transfected cell lines and the MN9D parent cells. Parameter Comparison p value Control Neurite Number MN9D/MN9D3    .008 Branch Number MN9D/MN9D3    .004 MN9D2/MN9D3    .003 MN9D3/MN9D4 <10⁻³ Quinpirole Branch Number MN9D/MN9D2 <10⁻³ MN9D/MN9D3 <10⁻⁶ MN9D/MN9D4    .002 MN9D3/MN9D4    .020 Primary Neurite Length MN9D/MN9D3 <10⁻³ (μm) MN9D/MN9D4 <10⁻⁴ MN9D2/MN9D3    .011 MN9D2/MN9D4 <10⁻⁴ Total Neuritic Extent MN9D/MN9D2    .035 (μm) MN9D/MN9D3 <10⁻⁶ MN9D/MN9D4 <10⁻⁵ MN9D2/MN9D4 <10⁻⁴

Quinpirole Enhances Morphological changes in Transfected Cells

[0057] The transfected dopamine D2-like receptor expressing cell lines have distinct morphologies. Since the parent MN9D cell line synthesizes and releases dopamine (Choi, H. K. Won, L. A., Kontur, L. A., et al, (1991) Brain Res. 552, 67-76) these 10 differences may be secondary to auto-stimulation of the expressed receptors by release of endogenous dopamine. To test whether further stimulation of receptors would result in increased morphological differences, cells were cultured in the presence of the dopamine D₂-like agonist quinpirole. This agonist was chosen for its high affinity for all three receptors and its low toxicity to neuronal cells.

[0058] Culture with quinpirole resulted in increased morphological differences between the transfected and parent cell lines. Differences between cell lines were apparent within 24 hours of exposure to quinpirole and lasted for at least 115 hours. Table 2 shows the results of a single experiment in which MN9D parent cells and the cell lines transfected with D_(b 2444), D₃ and D₄ receptors were cultured for 91 to 93 hours with and without 2 μM quinpirole. Compared to MN9D cells, stimulation of the transfected cell lines with quinpirole resulted in significant increases in the number of branches and extension of neurites (Table 3). Stimulation of D₂₄₄₄ receptors resulted in a four fold increase in the frequency of branching of neurites with little effect on neurite extension (n=100 cells for each condition, significance levels given in Table 3). D₃ receptor stimulation resulted in increases in neurite branching and neurite length (n=59 cells for each condition). D₄ receptor stimulation resulted in a small increase in neurite branching and a large increase in neurite extension (n=100 cells for each condition). These effects have been observed in three independent experiments for each receptor expressing cell line, as depicted in FIGS. 5A, B, C, and D. Treatment of the MN9D parent cells with 2 μM quinpirole resulted in no increases in neuritic outgrowth with the exception of the neurite number. As shown in Table 2, in this experiment there was a small but statistically significant increase in neurite number. However, in two other experiments, no significant differences in any morphological parameter were found on stimulation of MN9D cells (n=100 cells per condition for each experiment).

[0059] The effects of quinpirole stimulation varied with receptor subtype, as compared to the unstimulated state of each cell line. As shown in FIGS. 5A, 5B and 5C, D₂₄₄₄ stimulation resulted in significant percent increases in neurite number and branch number with only a small increase in neurite length. D₄ stimulation resulted in the largest percent increase in neurite length with no effect on neurite number. D₃ stimulation resulted in marked increases in branch number and neurite length with no effect on neurite number.

[0060] In summary, though the D₃ expressing MN9D cell line had more differentiated neurites in the unstimulated state, the D₂₄₄₄ expressing cell line showed larger increase in neurite length following quinpirole stimulation. On average, as compared to untransfected MN9D cells, the morphological effects of transfection and stimulation are that D₂₄₄₄ expressing MN9D cells have more branched neurites while D₄ expressing cells have longer less branched neurites. Stimulated, D₃ expressing MN9D cells have the most highly branched neurites and the longest total neuritic extents. The effects of quinpirole stimulation of all three receptors can be blocked by 1 μM eticlopride. Similar results have been found for quinpirole stimulation of primary cultures of dopaminergic, mesencephalic neurons which express a mixture of receptor subtypes, as shown by FIG. 6.

[0061] In conclusion, dopamine D₃-like receptors transfected into a clonal mesencephalic cell line regulate neurite outgrowth in these cells and the D₂ receptor subtypes appear to modulate different aspects of neurite outgrowth. These results suggest a role for dopamine D₂-receptors in mammalian neurodevelopment and provide support for the possibility that dopamine receptor subtypes differentially modulate neurite outgrowth in vivo. The observation of similar effects on neurite outgrowth in primary mesencephalic cultures supports the relevance of these effects for normal and abnormal brain development.

[0062] Assuming these responses occur in vivo, then fundamental changes in the anatomy and function of mesocortical and mesostriatal pathways could occur via abnormal receptor stimulation. These are the same brain regions where neuropathological and neuroimaging abnormalities have been reported for disorders such as schizophrenia (Benes, F. M., Davidson, J. and Bird, E. D. (1986) Arch. Gen. Psychiatr. 43, 31-35; Jeste, D. V. and Lohr, J. B. (1989) Arch. Gen. Psychiatr. 46, 1019-1024; Pfefferbaum, A. et al. (1988) Arch. Gen. Psychiatr. 45, 633-640. The results also indicate that developmental stimulation or inhibition of dopamine receptor subtypes via drugs, both therapeutically and abusively, can result in profound pre- and postnatal changes in neuronal morphology and function. Developmental regulation of receptor stimulation therefore offers a therapeutic approach to preventing or reversing neuroanatomical changes associated with a variety of neurological and psychiatric diseases.

EXAMPLE 5 Use of the Rat D₄ as a Screen for Cardiovascular Drugs and Other Biologically Useful Compounds

[0063] The cDNA orgene the D₄ dopamine receptor can be expressed in a variety of mammalian cell lines, including the fibroblast cell line described above, or in other commercially available cell lines such as Cos cells, and used to screen for compounds which bind specifically to the D₄ receptor. This is determined by comparing binding affinities for the various D₁, D₂, and D₃ receptors with that of the D₄ receptor, then testing in vivo those compounds which specifically bind the receptor. It can also be expressed in bacterial cells, notably E. coli, as well as other eukaryotic expression system such as Baculovirus infection of insect cells.

[0064] Based on the discovery that the D₄ dopamine receptor is predominantly associated with cardiovascular and retinal tissues, a principle use for this screen is for compounds having an effect on the cardiovasculature and retina, either dopamine antagonists or dopamine agonists, that act as vasoregulators or have ionotropic effects and that act on retinal cyclic AMP levels. Compounds which bind either the human or the rat D₄ dopamine receptor can be screened. The typical models for physiological testing of these compounds are rats, mice and dogs. Measurements can be made in intact animals, in cardiovascular and retinal tissue explants or in isolated cells.

[0065] The gene and/or cDNA can also be used to generate probes for screening in a manner similar to those methods described above for receptors other than the known D₁, D₂, D₃, and D₄ dopamine receptors. Probes are created from sequences generally fourteen to seventeen nucleotides in length, and can be labelled using available technology and reagents, including radiolabels, dyes, tomography position emission labels, magnetic resonance imaging labels, enzymes, and fluorescent labels. Probes can be used directly or indirectly via standard methodologies including polymerase chain reaction (PCR) and methodologies to generate larger fragments of the D4 receptor. Starting with either RNA (via RTI PCR) or DNA, the D4 cDNA, and parts therein, can also be used to generate RNA transcripts if cloned into appropriate expression vectors (cRNAs).

[0066] D4 DNA fragments, oligonucleotide probes or cRNAs, could all be used in commercial kits or sold separately to measure D4 transcript levels using standard techniques including PCR, in situ hybridization, and RNAse or SI protection assays.

[0067] Amino acid sequence can be deduced from fragments of D4, or the entire D4 coding sequence, generated by a variety of standard , techniques for synthesis of synthetic peptides, D4 fusion proteins and/or purification of D4 proteins (or parts thereof) from in vitro translated proteins derived from synthetic D4 RNA or protein purification per se. D4 proteins, peptides, fusion proteins or fragments thereof could subsequently be used for antibody production using available technology including injection into a wide variety of species including mice, rats, rabbits, guinea pigs, goats, etc. for the production of polyclonal antisera as well as injection into mice and subsequent utilization of fusion techniques for the production of monoclonal antibodies.

[0068] Oligonucleotides or larger sequences derived from the D4 mRNA or complementary sequences or antibodies directed against the D4 receptor could be labelled or derivatized to be used as imaging agents for position omission tomography (PCT) or magnetic resonance imaging (MRI) of the location of D4 receptors in vivo and in vitro.

[0069] Promoter sequences associated with the rat D4 receptor (5′ flanking sequences) may be utilized to create transgenic (non-human) animals via standard methodologies, for example, by microinjection into embryos or homologous recombination in embryonic stem cells. Depending upon the reporter gene utilized (Lac z, diptheria toxin, cholera toxin etc.) various animal models can be created leading to the overexpression or loss of D4 receptor activity. Additionally, promoter sequences driving foreign gene products such as the SW40 large T antigen could be used to create immortalized cell lines from D4-expressing cell types. Selected use of other foreign reporter genes can be used to make model systems whereby central nervous system or peripheral physiology can be modified. Finally, from the sequence information presented in sequences 1 and 2, vectors can be generated for subsequent homologous recombination experiments in which the D4 gene is inactivated or “knocked out”, allowing determination of the physiological role of the D4 gene.

[0070] Antibodies against the D4 receptor can be used for immunocytochemical localization, flow cytometry identification and isolation of D4 receptor expressing cells. Antibodies can also be used to block or modify the effects of D4 receptor agonists and antagonists both in vivo and in vitro.

[0071] The present invention is further understood by reference to the following nucleotide and amino acid sequences.

[0072] Sequence 1 is the nucleotide sequence for coding and protein coding regions of the rat D4 receptor gene loci.

[0073] Sequence 2 is the derived amino acid sequence for the rat D4 receptor gene loci

[0074] Sequence 3 is the nucleotide sequence for the human D4 receptor gene.

[0075] Sequence 4 is the derived amino acid sequence for the human D4 receptor gene.

[0076] Sequences 5-14 are oligonucleotide primers used in the isolation of the rat D4 receptor gene.

[0077] Sequence 15 is the nucleotide sequence for the rat D2 receptor gene.

[0078] Sequence 16 is the nucleotide sequence for the human D3 receptor gene.

1 16 1 3907 DNA Artificial Sequence misc_feature (1)..(3907) Rat D4 Gene 1 gatcccaagc gttgttccct atctgcccat gcgtgggtgt cggatgaaga gtgagcttga 60 tgtgcccgat tgttcagtat tgctgagcct agaaccctta gagaaagaga ggaggagcct 120 tagcctgtta cagaaccaga gttgatggtt tcctacgtgg aaggacccaa atgcaggagt 180 ccaatagttc caccacgtcc tccaaggtat cttggagaga cgcttttgac aagcaattta 240 gtggcctgtc tcctcgacgg gatgactgac tctgacgaat ctggtccaga caacctgctt 300 tccatatagt tttctggaag cacaaactaa cctggatcag gggaaacatc agtcgctgct 360 ccacctttta tgccagtcac tttgctcttg aattgaagca tttctccctc tgccaatttc 420 ctagagtgca gaaattcaag ccgtggcggg cggggcggag ctggacgctg ggggcgggat 480 tccggatagc ccctgactgc aaatccccag gctcagcgcc ttgcagagtc tcagctaggg 540 cgccatgggg aacagcagcg ctactggtga cggtgggctg ttggccgggc gtgggccaga 600 gtccttaggt actggcaccg gacttggggg cgcgggcgcg gcggcgctgg tgggaggcgt 660 gctgctcatc ggcatggtgt tggcagggaa ctcgctcgtt tgcgtgagcg tggcctccga 720 gcgcatcctg cagacaccca ccaactactt catcgtgagc ctggcggctg ccgacctcct 780 cctcgcggtg ctggtgttgc ctctctttgt ctactccgag gtgagcctcg gtgcactctt 840 tccctagctc catggctccc agcaccccag ccccagcgcg gtttcacgct tagaccctca 900 gcaaccttga gccagggggt ttgcagggac gccaggtctc ctcactcctg actacccact 960 ttctcccgct cttcagaatc tttcgcctac ttttcctccg tcaccctacc atcctctgaa 1020 tcccttccta ttctatctaa gatctgccaa cccagagagg actcgtgtcc ctaaaaccaa 1080 ggatcacaga aaaatgtctt tcctatttaa gccctggctc ccactgcaga aatactgcac 1140 ccccagcccc cgccaaaagc ctgctagaca ggcaggcgaa tgtgcagaca cacatcactg 1200 ccaatgacca ctgccttttg ggaacacaca cacacacaca cacacacaca cacacacacg 1260 ccagcctgtg ccagctcacc ctaaggaaga agccccaaag cccgcagcca cccagatgcc 1320 aggagcttgg agcattgcag gctgcaggca gagagggcct gggcaggata ctcaacctga 1380 ggggcttaaa gggagtgggt tcgggacctt ttggagacta ttggaacaga ggcaccccag 1440 atcaggtcct tctcttaggt gggactgctg tggttaccgg caactcttca tctgcccgag 1500 gtttggccac attaaaactg tttgggatag gggtgaggac aaagcagcct ggctggggga 1560 gagtgggaat aggaatgggg acatagtggc ctggactggg gaaagtgggg tgggatgcgc 1620 ggtatttcta aggaagagcc tgagttctgg agcagagcca gtggccacac ttgaccctag 1680 gtcctccccc aaggcacaga cgtcactggg atgattctta agctcctaat cgtcccgaat 1740 cagtgtgaag ggatttgggg atgggtggtt tgaggtggct gcatgctcct ttgcccttga 1800 aaacgaatac tccatgctgc agactcacag agaagctcat gaggtctttg tacttttagg 1860 acacacttgt cctcaggaca attgtcatat gtccagcaag tgaagagacc tattcaaagc 1920 tccacagcag tgacagttca tgcaggcagg ataacgtgcg tgttggaagt ggataggatt 1980 tgtgtttagg gggtgaaggg tcaggcctaa gaatgcaggg gctcctctcc ctcagatggt 2040 attatcctct cggatcttac ccgagctttt cacctaaaca aaagacctaa gtcaagaggc 2100 aggtctgttt gccccctctg tcctcagttt acacttgtct ccaacacatg tctcaggctc 2160 actttgggct ggtacgcccc ctcccctcta acacacagcc ctccactccc ctcaacaaga 2220 gcgggggggt cagaaagccc gccgctgaaa ggtcaggtct tgtgtttcat ttctgcaacc 2280 tcttcgtggc caggtccagg gtggcgtgtg gctgctgagc ccccgcctct gtgacaccct 2340 catggccatg gacgtcatgc tgtgcaccgc ctccatcttc aacctgtgcg ccatcagcgt 2400 ggacaggtgg gtaccccgga cgacccgtct cttccattcc catcttccgg tcagctgctc 2460 cattcggcgg cctcaccact cctgtgctcc ttcctctagg tttgtggctg tgaccgtgcc 2520 actgcgctac aaccagcagg gtcagtgcca gctgctgctc atcgccgcca cgtggctgct 2580 gtctgccgcg gtggctgcgc ccgtcgtgtg cggcctcaat gatgtgcccg gtcgcgatcc 2640 aaccgtgtgc tgcctggagg accgcgacta cgtggtctac tcatccattt gttccttctt 2700 cctgccctgt ccgctcatgc tactgcttta ctgggccact ttccgtggct tgcggcgctg 2760 ggaggcagcc cggcacacca agcttcacag ccgcgcgccg cgccgaccca gcggcccggg 2820 cccgccggtg tcggacccta ctcagggtcc cctcttctca gattgtccgc ctccctcacc 2880 cagcctccgg acgagcccca ccgtctccag cagaccagag tcagacctct ctcagagccc 2940 ctgcagcccc gggtgtctgc tccctgatgc agcgctcgcg caaccgcctg cgccgtcttc 3000 ccgcagaaag agaggcgcca agatcactgg aagggagcgc aaggcgatga gagtcctgcc 3060 ggtggtagtt ggtgggtttc cgccctggga caagagctga tagagggagg ggtcccggga 3120 gccgaggagg gaagggggaa gggtccagtt tggaagggtg aaaggtgggg gacgggggtt 3180 cctggttgag agacctcgag tgcaggtgtc ctgggtgagg gaccttgagt gcaggtgtat 3240 agctcacgcc gcccaccccc aggccccttc ctgatgtgtt ggacgccttt cttcgtggtg 3300 cacatcacac gggcgctgtg tccggcttgt ttcgtgtccc cacgcctggt cagtgctgtc 3360 acctggctgg gctatgtcaa cagtgccctc aaccccatca tctacaccat cttcaatgcc 3420 gagtttcgaa gtgtcttccg caagactctt cgtctccgct gctgaaagaa ccgctgatgt 3480 cttgaggtca aggggttcca agcctgtgtg cagagtgcgc tggcggcttt cgttcgtctg 3540 attaaatgaa gtctttccta accatttatc aacgctgggg gctgggaaaa agtaaggaaa 3600 agagggaggt cttttgtctg gatgatgggc ccggctaact tctgcctttg aggatgctgc 3660 cggttcagct ccaggaggca ggaggcttca gaagtctttg ccctggagga gtaggggacc 3720 gactacatct gccttagttt ccgctcaaca tgaaaaatga ccaagtgttc tcctgggaga 3780 ggagctagag gaatttcctg aggctcctgg gtccccagga tcctgtccag gccttgctcc 3840 ttggagagct agggagggag ggctcttctg tcattgatgg gggaggggat tcccatttca 3900 gaagctt 3907 2 385 PRT Rattus norvegicus PEPTIDE (1)..(385) Protein encoded by cDNA for D4 receptor 2 Met Gly Asn Ser Ser Ala Thr Gly Asp Gly Gly Leu Leu Ala Gly Arg 1 5 10 15 Gly Pro Glu Ser Leu Gly Thr Gly Thr Gly Leu Gly Gly Ala Gly Ala 20 25 30 Ala Ala Leu Val Gly Gly Val Leu Leu Ile Gly Met Val Leu Ala Gly 35 40 45 Asn Ser Leu Val Cys Val Ser Val Ala Ser Glu Arg Ile Leu Gln Thr 50 55 60 Pro Thr Asn Tyr Phe Ile Val Ser Leu Ala Ala Ala Asp Leu Leu Leu 65 70 75 80 Ala Val Leu Val Leu Pro Leu Phe Val Tyr Ser Glu Gly Gly Val Trp 85 90 95 Leu Leu Ser Pro Arg Leu Cys Asp Thr Leu Met Ala Met Asp Val Met 100 105 110 Leu Cys Thr Ala Ser Ile Phe Asn Leu Cys Ala Ile Ser Val Asp Arg 115 120 125 Phe Val Ala Val Thr Val Pro Leu Arg Tyr Asn Gln Gln Gly Gln Cys 130 135 140 Gln Leu Leu Leu Ile Ala Ala Thr Trp Leu Leu Ser Ala Ala Val Ala 145 150 155 160 Ala Pro Val Val Cys Gly Leu Asn Asp Val Pro Gly Arg Asp Pro Thr 165 170 175 Val Cys Cys Leu Glu Asp Arg Asp Tyr Val Val Tyr Ser Ser Ile Cys 180 185 190 Ser Phe Phe Leu Pro Cys Pro Leu Met Leu Leu Leu Tyr Trp Ala Thr 195 200 205 Phe Arg Gly Leu Arg Arg Trp Glu Ala Ala Arg His Thr Lys Leu His 210 215 220 Ser Arg Ala Pro Arg Arg Pro Ser Gly Pro Gly Pro Pro Val Ser Asp 225 230 235 240 Pro Thr Gln Gly Pro Leu Phe Ser Asp Cys Pro Pro Pro Ser Pro Ser 245 250 255 Leu Arg Thr Ser Pro Thr Val Ser Ser Arg Pro Glu Ser Asp Leu Ser 260 265 270 Gln Ser Pro Cys Ser Pro Gly Cys Leu Leu Pro Asp Ala Ala Leu Ala 275 280 285 Gln Pro Pro Ala Pro Ser Ser Arg Arg Lys Arg Gly Ala Lys Ile Thr 290 295 300 Gly Arg Glu Arg Lys Ala Met Arg Val Leu Pro Val Val Val Gly Pro 305 310 315 320 Phe Leu Met Cys Trp Thr Pro Phe Phe Val Val His Ile Thr Arg Ala 325 330 335 Leu Cys Pro Ala Cys Phe Val Ser Pro Arg Leu Val Ser Ala Val Thr 340 345 350 Trp Leu Gly Tyr Val Asn Ser Ala Leu Asn Pro Ile Ile Tyr Thr Ile 355 360 365 Phe Asn Ala Glu Phe Arg Ser Val Phe Arg Lys Thr Leu Arg Leu Arg 370 375 380 Cys 385 3 1367 DNA Homo sapiens misc_feature (1)..(1367) D4 Dopamine Receptor cDNA 3 cgggggcggg accagggtcc ggccggggcg tgcccccggg gagggactcc ccggcttgcc 60 ccccggcgtt gtccgcggtg ctcagcgccc gcccgggcgc gccatgggga accgcagcac 120 cgcggacgcg gacgggctgc tggctgggcg cgggccggcc gcgggggcat ctgcgggggc 180 atctgcgggg ctggctgggc agggcgcggc ggcgctggtg gggggcgtgc tgctcatcgg 240 cgcggtgctc gcggggaact cgctcgtgtg cgtgagcgtg gccaccgagc gcgccctgca 300 gacgcccacc aactccttca tcgtgagcct ggcggccgcc gacctcctcc tcgctctcct 360 ggtgctgccg ctcttcgtct actccgaggt ccagggtggc gcgtggctgc tgagcccccg 420 cctgtgcgac gccctcatgg ccatggacgt catgctgtgc accgcctcca tcttcaacct 480 gtgcgccatc agcgtggaca ggttcgtggc cgtggccgtg ccgctgcgct acaaccggca 540 gggtgggagc cgccggcagc tgctgctcat cggcgccacg tggctgctgt ccgcggcggt 600 ggcggcgccc gtactgtgcg gcctcaacga cgtgcgcggc cgcgaccccg ccgtgtgccg 660 cctggaggac cgcgactacg tggtctactc gtccgtgtgc tccttcttcc taccctgccc 720 gctcatgctg ctgctctact gggccacgtt ccgcggcctg cagcgctggg aggtggcacg 780 tcgcgccaag ctgcacggcc gcgcgccccg ccgacccagc ggccctggcc cgccttcccc 840 cacgccaccc gcgccccgcc tcccccagga cccctgcggc cccgactgtg cgccccccgc 900 gcccggcctc cccccggacc cctgcggctc caactgtgct ccccccgacg ccgtcagagc 960 cgccgcgctc ccaccccaga ctccaccgca gacccgcagg aggcggcgtg ccaagatcac 1020 cggccgggag cgcaaggcca tgagggtcct gccggtggtg gtcggggcct tcctgctgtg 1080 ctggacgccc ttcttcgtgg tgcacatcac gcaggcgctg tgtcctgcct gctccgtgcc 1140 cccgcggctg gtcagcgccg tcacctggct gggctacgtc aacagcgccc tcaaccccgt 1200 catctacact gtcttcaacg ccgagttccg caacgtcttc cgcaaggccc tgcgtgcctg 1260 ctgctgagcc gggcaccccc ggacgccccc cggcctgatg gccaggcctc agggaccaag 1320 gagatgggga gggcgctttt gtacgttaat taaacaaatt ccttccc 1367 4 387 PRT Artificial Sequence PEPTIDE (1)..(387) Human D4 Receptor Protein 4 Met Gly Asn Arg Ser Thr Ala Asp Ala Asp Gly Leu Leu Ala Gly Arg 1 5 10 15 Gly Pro Ala Ala Gly Ala Ser Ala Gly Ala Ser Ala Gly Leu Ala Gly 20 25 30 Gln Gly Ala Ala Ala Leu Val Gly Gly Val Leu Leu Ile Gly Ala Val 35 40 45 Leu Ala Gly Asn Ser Leu Val Cys Val Ser Val Ala Thr Glu Arg Ala 50 55 60 Leu Gln Thr Pro Thr Asn Ser Phe Ile Val Ser Leu Ala Ala Ala Asp 65 70 75 80 Leu Leu Leu Ala Leu Leu Val Leu Pro Leu Phe Val Tyr Ser Glu Val 85 90 95 Gln Gly Gly Ala Trp Leu Leu Ser Pro Arg Leu Cys Asp Ala Leu Met 100 105 110 Ala Met Asp Val Met Leu Cys Thr Ala Ser Ile Phe Asn Leu Cys Ala 115 120 125 Ile Ser Val Asp Arg Phe Val Ala Val Ala Val Pro Leu Arg Tyr Asn 130 135 140 Arg Gln Gly Gly Ser Arg Arg Gln Leu Leu Leu Ile Gly Ala Thr Trp 145 150 155 160 Leu Leu Ser Ala Ala Val Ala Ala Pro Val Leu Cys Gly Leu Asn Asp 165 170 175 Val Arg Gly Arg Asp Pro Ala Val Cys Arg Leu Glu Asp Arg Asp Tyr 180 185 190 Val Val Tyr Ser Ser Val Cys Ser Phe Phe Leu Pro Cys Pro Leu Met 195 200 205 Leu Leu Leu Tyr Trp Ala Thr Phe Arg Gly Leu Gln Arg Trp Glu Val 210 215 220 Ala Arg Arg Ala Lys Leu His Gly Arg Ala Pro Arg Arg Pro Ser Gly 225 230 235 240 Pro Gly Pro Pro Ser Pro Thr Pro Pro Ala Pro Arg Leu Pro Gln Asp 245 250 255 Pro Cys Gly Pro Asp Cys Ala Pro Pro Ala Pro Gly Leu Pro Pro Asp 260 265 270 Pro Cys Gly Ser Asn Cys Ala Pro Pro Asp Ala Val Arg Ala Ala Ala 275 280 285 Leu Pro Pro Gln Thr Pro Pro Gln Thr Arg Arg Arg Arg Arg Ala Lys 290 295 300 Ile Thr Gly Arg Glu Arg Lys Ala Met Arg Val Leu Pro Val Val Val 305 310 315 320 Gly Ala Phe Leu Leu Cys Trp Thr Pro Phe Phe Val Val His Ile Thr 325 330 335 Gln Ala Leu Cys Pro Ala Cys Ser Val Pro Pro Arg Leu Val Ser Ala 340 345 350 Val Thr Trp Leu Gly Tyr Val Asn Ser Ala Leu Asn Pro Val Ile Tyr 355 360 365 Thr Val Phe Asn Ala Glu Phe Arg Asn Val Phe Arg Lys Ala Leu Arg 370 375 380 Ala Cys Cys 385 5 18 DNA Artificial Sequence Description of Artificial Sequence primer- TM VI/VII primer set orD-403 5 tgctggctgc ccttcttc 18 6 18 DNA Artificial Sequence Description of Artificial Sequence primer- TM VI in both D2 and D3 genes and or D-404 6 gaagcctttg cggaactc 18 7 18 DNA Artificial Sequence Description of Artificial Sequence primer-reverse transcribed using orD4-515 and is complementary to nucleotides 2389-2406 in SEQ ID NO1 7 ctgtccacgc tgatggcg 18 8 18 DNA Artificial Sequence Description of Artificial Sequence primer-utilized orD4-465 and orD4-466 and is identical to nucleotides 731-748 in SEQ ID NO1 8 cagacaccca ccaactac 18 9 18 DNA Artificial Sequence Description of Artificial Sequence primer- included orD4-474 and is identical to nucleotides 2332-2349 in SEQ ID NO1 9 tgacaccctc atggccat 18 10 18 DNA Artificial Sequence Description of Artificial Sequence primer- included orD4-465 and is complementary to nucleotides 2365-2382 in SEQ ID NO1 10 ttgaagatgg aggcggtg 18 11 18 DNA Artificial Sequence Description of Artificial Sequence primer- included orD4-501 and is identical to nucleotides 2773-2790 in SEQ ID NO1 11 gcacaccaag cttcacag 18 12 22 DNA Artificial Sequence Description of Artificial Sequence primer- included orD4-506 and is complementary to nucleotides 3371-3392 in SEQ ID NO1 12 ttgagggcac tgttgacata gc 22 13 24 DNA Artificial Sequence Description of Artificial Sequence oligonucleotide included orD-502 and is identical to nucleotides 674-697 in SEQ ID NO1 13 atggtgttgg cagggaactc gctc 24 14 24 DNA Artificial Sequence Description of Artificial Sequence ologonucleotide included orD-499 and is complementary to nucleotides 674-697 in SEQ ID NO1 14 gagcgagttc cctgccaaca ccat 24 15 2428 DNA cDNA misc_feature (1)..(2428) Rat D2 receptor sequence 15 ccacccagtg gccccactgc cccaatggat ccactgaacc tgtcctggta cgatgacgat 60 ctggagaggc agaactggag ccggcccttc aatgggtcag aagggaaggc agacaggccc 120 cactacaact actatgccat gctgctcacc ctcctcatct ttatcatcgt ctttggcaat 180 gtgctggtgt gcatggctgt atcccgagag aaggctttgc agaccaccac caactacttg 240 atagtcagcc ttgctgtggc tgatcttctg gtggccacac tggtaatgcc gtgggttgtc 300 tacctggagg tggtgggtga gtggaaattc agcaggattc actgtgacat ctttgtcact 360 ctggatgtca tgatgtgcac agcaagcatc ctgaacctgt gtgccatcag cattgacagg 420 tacacagctg tggcaatgcc catgctgtat aacacacgct acagctccaa gcgccgagtt 480 actgtcatga ttgccattgt ctgggtcctg tccttcacca tctcctgccc actgctcttc 540 ggactcaaca atacagacca gaatgagtgt atcattgcca accctgcctt tgtggtctac 600 tcctccattg tctcattcta cgtgcccttc atcgtcactc tgctgctgta tatcaaaatc 660 tacatcgtcc tccggaagcg ccggaagcgg gtcaacacca agcgcagcag tcgagctttc 720 agagccaacc tgaagacacc actcaagggc aactgtaccc accctgagga catgaaactc 780 tgcaccgtta tcatgaagtc taatgggagt ttcccagtga acaggcggag aatggatgct 840 gcccgccgag ctcaggagct ggaaatggag atgctgtcaa gcaccagccc cccagagagg 900 acccggtata gccccatccc tcccagtcac caccagctca ctctccctga tccatcccac 960 cacggcctac atagcaaccc tgacagtcct gccaaaccag agaagaatgg gcacgccaag 1020 attgtcaatc ccaggattgc caagttcttt gagatccaga ccatgcccaa tggcaaaacc 1080 cggacctccc ttaagacgat gagccgcaga aagctctccc agcagaagga gaagaaagcc 1140 actcagatgc ttgccattgt tctcggtgtg ttcatcatct gctggctgcc cttcttcatc 1200 acgcacatcc tgaatataca ctgtgattgc aacatcccac cagtcctcta cagcgccttc 1260 acatggctgg gctatgtcaa cagtgccgtc aaccccatca tctacaccac cttcaacatc 1320 gagttccgca aggccttcat gaagatcttg cactgctgag tctgcccctt gcctgcacag 1380 cagctgcttc ccacctccct gcctatgcag gccagacctc atccctgcaa gctgtgggca 1440 gaaaggccca gatggacttg gccttctctc gaccctgcag gccctgcagt gttagcttgg 1500 ctcgatgccc ctctctgccc acacaccctc atcctgccag ggtagggcca gggagactgg 1560 tatcttacca gctctggggt tggacccatg gctcagggca gctcacagag tgcccctctc 1620 atatccagac cctgtctcct tggcaccaaa gatgcagcgg ccttccttga ccttcctctt 1680 gggcacagaa actagctcag tggtcgagca caccctgatc gctggcttgg cctggccctt 1740 gcttgcctgt gccagatcag gtggtgggag ggagcaacag ttcttacttt ataggaacca 1800 cataggaaag cagggaacac gccaagtcct ccaggcaaca tcagtgtcag gagacacaca 1860 taaacaccag gtagctccat ggaccccaga gaaactgagg ctgaaaaatc tgttttccac 1920 tccaactcta gtgtgagtcc ctacttttca tagccatggg tattactatg tcctaccttg 1980 ttatagtatc ccatggggtt tctgtaccat ttgggggaaa acaactctaa tcctcaaggg 2040 ccccaagaga atctgtaagg agaaaaatag gctgatctcc ctctactctc caatccactc 2100 caccacttct tgatatacct tggatgtatc cattcctcac agcaaatgct ggccagtcag 2160 gccttggacc agtgttggag ttgaagctgg atgtggtaac ttggggctct ttggggctgg 2220 gggggttgtt aacatcgtct ctcttccata tctcttcctt cccagtgcct ctgccttaga 2280 agaggctgtg gatggggtgc tgggactgct gataccattg ggcctggctg aatgaggagg 2340 ggaagctgca gtttggaggg ttctgggatc caactctgta acatcactat acctgcacca 2400 aaactaataa aaccttgaca agagtcaa 2428 16 1261 DNA Homo sapiens misc_feature (1)..(1261) Human d3 cDNA 16 tgggctatgg catctctgag tcagctgagt agccacctga actacacctg tggggcagag 60 aactccacag gtgccagcca ggcccgccca catgcctact atgccctctc ctactgcgcg 120 ctcatcctgg ccatcgtctt cggcaatggc ctggtgtgca tggctgtgct gaaggagcgg 180 gccctgcaga ctaccaccaa ctacttagta gtgagcctgg ctgtggcaga cttgctggtg 240 gccaccttgg tgatgccctg ggtggtatac ctggaggtga caggtggagt ctggaatttc 300 agccgcattt gctgtgatgt ttttgtcacc ctggatgtca tgatgtgtac agccagcatc 360 cttaatctct gtgccatcag catagacagg tacactgcag tggtcatgcc cgttcactac 420 cagcatggca cgggacagag ctcctgtcgg cgcgtggccc tcatgatcac ggccgtctgg 480 gtactggcct ttgctgtgtc ctgccctctt ctgtttggct ttaataccac aggggacccc 540 actgtctgct ccatctccaa ccctgatttt gtcatctact cttcagtggt gtccttctac 600 ctgccctttg gagtgactgt ccttgtctat gccagaatct atgtggtgct gaaacaaagg 660 agacggaaaa ggatcctcac tcgacagaac agtcagtgca acagtgtcag gcctggcttc 720 ccccaacaaa ccctctctcc tgacccggca catctggagc tgaagcgtta ctacagcatc 780 tgccaggaca ctgccttggg tggaccaggc ttccaagaaa gaggaggaga gttgaaaaga 840 gaggagaaga ctcggaattc cctgagtccc accatagcgc ctaagctcag cttagaagtt 900 cgaaagctca gcaatggcag attatcgaca tctttgaagc tggggcccct gcaacctcgg 960 ggagtgccac ttcgggagaa gaaggcaacc caaatggtgg ccattgtgct tggggccttc 1020 attgtctgct ggctgccctt cttcttgacc catgttctca atacccactg ccagacatgc 1080 cacgtgtccc cagagcttta cagtgccacg acatggctgg gctacgtgaa tagcgccctc 1140 aaccctgtga tctataccac cttcaatatc gagttccgga aagccttcct caagatcctg 1200 tcttgctgag ggagcagaag agggaacact ctttgtaccc atttctagct gccaggctgt 1260 t 1261 

We claim:
 1. An isolated nucleic acid molecule encoding a rat D₄ dopamine receptor.
 2. The molecule of claim 1 further comprising the flanking 5′ and 3′ untranalated sequences.
 3. The molecule of claim 1 wherein the molecule includes the untranslated introns of the derived gene.
 4. The molecule of claim 1 consisting essentially of sequence ID No.
 1. 5. The molecule of claim 1 encoding the protein consisting essentially of sequence ID No.
 2. 6. The molecule of claim 1 in an expression cell system.
 7. The molecule of claim 6 in a non-rat D4 expressing cell.
 8. A probe for dopamine receptors comprising at least fourteen contiguous nucleotides of a nucleic acid molecule encoding a rat D₄ dopamine receptor as shown in Sequence ID No.
 1. 9. The probe of claim 8 further comprising a label selected from the group consisting of dyes, radiolabels, tomography positron emission labels, magnetic resonance imaging labels, fluorescent labels, and enzymes.
 10. A method for screening for compounds selectively binding to a rat D₄ dopamine receptor comprising transfecting cells with an isolated nucleic acid molecule encoding a rat D₄ dopamine receptor, exposing the cells expressing the dopamine receptor to compounds which may bind to the receptor, selecting those compounds binding to the receptor, comparing the binding of the selected compounds with the binding of the compounds to other dopamine receptors, and determining which compounds bind to the D₄ dopamfine receptor but with lower affinity to other dopamine receptors.
 11. The method of claim 10 further comprising administering the compounds to a biological material selected from the group consisting of animals, tissue explants, and individual cells and determining the effect on the physiology of the material.
 12. A method for screening for compounds selectively acting on tissue selected from the group consisting of the cardiovascular and retinal systems by binding to dopamine receptors comprising transfecting cells with a nucleic acid molecule encoding a D₄ dopamine receptor, and determining if compounds bind to the receptor and not to other dopamine receptors with the same affinity, administering the compounds with the desired binding affinity to a biological material selected from the group consisting of animals, tissue explants, and individual cells and measuring effects on cardiovasculature and retinal physiology.
 13. The method of claim 12 wherein the D₄ dopamine receptor is selected from the group consisting of human and rat D₄ dopamine receptors.
 14. The method of claim 12 wherein the other dopamine receptors are selected from the group consisting of human and rat D₂ and D₃ receptors.
 15. A method for altering the morphology of mammalian cells comprising stimulating or inhibiting a dopamine receptor selected from the group consisting of D₂, D₃, and D₄ receptors.
 16. The method of claim 15 wherein the cells do not normally express the dopamine receptor or wherein the cells do not normally express as many molecules of the dopamine receptor.
 17. The method of claim 15 wherein the cells are neuronal cells.
 18. The method of claim 15 wherein the dopamine receptors are selectively stimulated by exposure to an effective amount of a compound selected from the group consisting of dopamine antagonists and dopamine agonists.
 19. The method of claim 15 wherein the expression of the receptors is selected to alter the morphology of the cells.
 20. The method of claim 17 wherein the cells are stimulated by a compound binding to the dopamine receptors so that the neurites increase the number and extension of the neurites.
 21. The method of claim 19 wherein the cells are stimulated by exposure to a compound selected from the group consisting of dopamine agonists, dopamine antagonists, antibodies to D₄, and combinations thereof.
 22. An antibody immunoreactive with the rat D₄ receptor.
 23. The antibody of claim 21 selected from the group consisting of polyclonal and monoclonal antibodies which recognize the D₄ receptor sequence but do not recognize D₁, D₂, D₃ and D₅ dopamenergic receptors.
 24. A method for treating disorders of the cardiovasoulature or retinal tissue comprising administering a compound selectively binding to D₄ receptors to a patient in need of treatment in an amount effect to decrease the symptoms of the disorder.
 25. The method of claim 23 wherein the compound modulates the degree of vasoconstriction.
 26. A method for treating disorders of neuronal morphology or connections comprising administering a compound selectively binding to D₂, D₃, or D₄ receptors to a patient in need of treatment thereof in an amount effective to decrease the symptoms of the disorder.
 27. A method for preventing the development of disorders of neuronal morphology or connections comprising administering a compound selectively binding to D₂, D₃, or D₄ receptors to a patient at risk thereof in an amount effective to prevent or delay the onset of evidence of the disorder.
 28. The method of claim 27 wherein the compound is selected from the group of compounds modulating the number, branching, or outgrowth or neurites. 